A process for the preparation of substituted aromatic compounds employing Friedel-Crafts reaction and using a basic anionic clay hydrotalcite-type solid catalyst. This invention particularly relates to a process for the alkylation or acylation of aromatic compounds by an alkylating or acylating agent for preparing alkylated or acylated aromatic compounds, using basic anionic clay hydrotalcite-type solid catalyst.
The process for this invention could be used for the preparation of alkylated or acylated aromatic compounds, which are fine chemicals and/or used as intermediates in the preparation of fine chemicals or specialty chemicals in dyes and pharmaceutical industries and other chemical industries.
Both the homogeneous and heterogeneous catalyzed liquid phase Friedel-Crafts processes for the preparation of alkylated and acylated aromatic compounds are known in the prior art.
Friedel-Crafts Type Reactions Catalysed by Homogeneous Acid Catalysts
The Friedel-Crafts type reactions, such as alkylation and acylation of aromatic compounds by various alkylating or acylating agents, using homogeneous Lewis acid catalysts, such as AlCI3, BF3, ZnCl2 and other metal chlorides and protonic acid catalysts, such as H2SO4, H3PO4, HF, etc., are well known in the prior art [ref. G. A. Olah, in Friedel-Crafts and related reactions: vol. III, Acylation and related reactions, Wiley-Interscience Publ., New York, 1964].
A use of CuCl2 as a homogeneous catalyst in the benzylation of benzene or substituted benzenes by benzyl chloride is disclosed in two US patents: U.S. Pat. No. 3,678,122(1972) and U.S. Pat. No. 3,679,760(1972). A French patent, FR 2,144,578(1973), disclosed benzylation of p-substituted phenols by benzyl halides in the presence of homogeneous ZnCl2 catalyst. A USSR patent, U.S.S.R. 394,353(1973), disclosed a use of SnSO4 or SnCl2 as homogeneous catalyst for the benzylation with benzyl chloride of m-dimethoxy benzene. A Japanese patent, JP 7399,154(1973), disclosed preparation of dibenzyl benzene derivatives by benzylation of benzene or substituted benzenes using AlC3, FeCl3 and 98% H2SO4. A use of H2SO4 or H3PO4 and optionally 4-CH3C6H4SO3H, ZnCl2, BF3, etc. in the preparation of o-benzyltoluenes by the reaction of xcex1 o-chloromethyltoluene with a benzene derivative is disclosed in a German patent, Ger. Offen 2,456,747 (1976). A use of phosphoric acid and optionally H2SO4 or a Friedel-Crafts type metal halide in the benzylation of benzene with benzylether is disclosed in a U.S. Patent, U.S. Pat. No. 4,049,733 (1977).
A German patent, Ger.offen 2,451,037 (1976), disclosed the use of HF as a catalyst for the benzoylation of aromatic compounds.
A French patent, FR 2,496,097 (1982) disclosed the acylation of benzene by phthalic anhydride using HF-BF3 mixture.
More recently, an European Patent, EP 538,704 (1993), disclosed a process for the preparation of p-substituted o-benzylphenols by treating phenols, p-R C6H4OH (R=halo, alkyl, OH, alkoxy, alkylmercapto, aryl, aryloxy or arylmercapto), with ArCH2X (Ar=corresponding aryl nucleus; X=halo, arylcarboxy, phenylsulfatoxy, hydroxy, alkoxy etc.) in a continuously functioning distillation apparatus in the presence of dissolved acid catalyst.
The main disadvantages of the Friedel-Crafts processes based on the use of homogeneous acid catalyst are as follows:
1) The separation and recovery of the dissolved acid catalysts from the liquid reaction mixture is difficult.
2) The disposal of the used acid catalysts creates environmental pollution.
3) The homogeneous acid catalysts also pose several other problems such as high toxicity, corrosion, spent acid disposal and use of more than the stoichiometric amount.
Friedel-Crafts Type Reactions Catalysed by Heterogeneous Solid Acid Catalysts
A German patent, Ger.Offen 2,547,030 (1977), disclosed the preparation of o-benzyl toluenes by the reaction of o-methylbenzyl halides with substituted benzenes in the presence of Al-silicate. The 2-CH3C6H4CH2Cl was stirred with toluene and Al-silicate (25% Al2O3) at 110xc2x0 C. to give 81% 2-methylbenzyltoluene. According to a Japanese patent, JP 59,186,937 (1984), o-benzylphenol was prepared by the liquid phase reaction of benzyl alcohol with phenol in the presence of xcex3-Al2O3. For example 7.5 g xcex3-Al2O3 was added to a mixture of 32.5 g benzyl alcohol and 47 g phenol at 190xc2x0 C. under stirring to give a product-containing 49.9% o-benzylphenol. A German Patent, Ger. Offen DE 3,700,917 (1988), disclosed the preparation of p-substituted o-benzylphenols by alkylation of p-substituted phenols with benzylalcohol in the presence of Na-Y type zeolite. A mixture of 0.5 mole 4-ClC6H4OH, 0.1 mole C6H5CH2OH and 0.6 g of Na-Y type zeolite was heated at 200xc2x0 C. for 3 hrs to give 25.4% 2-benzyl-4-chlorophenol.
A French patent, FR 2,667,063 (1992), disclosed the preparation of 4-substituted benzophenones by acylation of substituted benzenes by substituted benzoic acid in the presence of Hxcex3-and Hxcex2 type zeolites. Accordingly, 4-ClC6H4COOH and PhMe were heated 4 h at 200xc2x0 C. under 2xc3x97105 Pa in the presence of calcined zeolite Hxcex2 to give 84.4% 4-(4-Cl C6H4CO)C6H4 Me.
A recent paper by Vincent et al. (ref. Tetrahedron Lett. 35, 1994, 2601), disclosed that H-ZSM-5 zeolite can catalyze the acylation by benzoyl chloride of phenol and anisole but not the acylation with benzoyl chloride of benzene, halobenzene and naphthalene, at 120xc2x0 C. for 5 h.
A German patent, Ger. Offen DE 3,836,780 (1990), disclosed the process for the preparation of benzylbenzenes from benzenes and benzyl alcohols in the presence of activated bleaching earth and a diluent at 90-140xc2x0 C. According to Japanese patent, JP 03,170,442 (1991), benzylbiphenyls are manufactured by alkylating biphenyl and diphenylmethane with xe2x89xa71 compound from benzyl halides, benzyl alcohol, benzyl ether in the presence of a zeolite or silica-alumina catalyst. An European patent, EP 428,081 (1991), disclosed a process of alkylation of alkylbenzenes with benzyl chloride in the presence of H-Y or H-L zeolite catalyst. A German patent, Ger. Offen DE 4,038,933 (1992), disclosed a process for alkylation of aromatics using technical carbon catalysts.
Alkylation or acylation of aromatic compound involves electrophilic substitution of H from the aromatic nucleus of the aromatic compound. It is well known in the prior art that the electrophilic substitution is favored by the presence of electron donating groups, such as OH, alkyl, alkoxy, phenoxy, amine, alkyl amine, SH, etc., in the aromatic compound. Whereas the electrophilic substitution is inhibited by the presence of electron withdrawing groups such as halo, nitro, cyano, carboxy, aldehyde, etc., in the aromatic compound [ref G. A. Olah, in Friedel-Crafts and related reactions, Wiley-Interscience Publ, New York, 1963].
Although some limitations of the homogeneous acid catalyzed processes are overcome in the prior art of heterogeneous solid catalyzed processes described above, the alkylating or acylating activity of the solid acid catalysts used in the prior art processes is low, particularly when no electron donating group is present in the aromatic compound, such as benzene, naphthalene and anthracene, to be alkylated or acylated. Both the homogeneous and heterogeneous acid catalysts of the prior art are highly moisture sensitive, and hence demand moisture-free or thoroughly dried reactants, solvents and catalyst for the Friedel-Crafts processes. In presence of moisture in the reaction mixture, both the above homogeneous and heterogeneous catalysts show poor activity in the Friedel-Crafts type processes. Hence there is a great practical need for finding more efficient and also moisture insensitive solid catalyst for the alkylation or acylation of aromatic compounds. There is also a need for finding highly efficient non-acidic or basic solid catalyst for alkylating or acylating aromatic compounds, which are acid sensitive.
This invention is made with the following objects so that most of the drawbacks or limitations of the prior art homogeneous and heterogeneous catalyzed processes for the Friedel-Crafts type alkylation or acylation reactions could be overcome.
The main object of this invention is to provide a liquid phase process for the alkylation or acylation of aromatic compounds, including those not containing electron donating groups, using a basic anionic clay hydrotalcite-type catalyst, which has high activity not only when the aromatic ring activating groups (i.e. electron donating groups such as alkyl, alkoxy, hydroxy, phenoxy, etc) are present in the aromatic ring to be alkylated or acylated but also when the ring activating group in the aromatic ring to be alkylated or acylated is absent, so that the reaction temperature is low and/or time for completing the reaction is short.
Other important object of this invention is to provide a liquid phase process for the alkylation or acylation of aromatic compounds, using a basic anionic clay hydrotalcite-type solid catalyst which is easily separable and reusable in the process for several times.
Another important object of this invention is to provide a solid catalyzed liquid phase process for the alkylation or acylation of aromatic compounds even in the presence of moisture in the reaction mixture.
A process for Friedel-Crafts type liquid-phase alkylation or acylation of an aromatic compound using a hydrotalcite-type basic anionic clay catalyst represented by a formula:
[(M2+)1xe2x88x92x(M3+)x(OH)2]x+[Ayxe2x88x92]x/y q H2O
where
M2+ is a divalent cation selected from Mg2+, Zn2+ Ni2+, Co2+, Mn2+, Cu2+ or a mixture thereof;
M3+ is a trivalent cation selected from Ga3+, In3+, Al3+, Fe3+ Cr3+ or a mixture thereof; x is a mole fraction of trivalent cations in the range of about 0.05 to about 0.5; O is oxygen; H is hydrogen; Ayxe2x88x92 is an anion; y minus is an anionic negative charge having a value of 1 minus or 2 minus; and q is a number of water molecules, as the water of hydration; said process comprising the following steps:
i. pretreating said catalyst by contacting it with a halogen containing compound in the presence or absence of a non-aqueous solvent and optionally washing the pretreated catalyst with non-aqueous solvent or liquid aromatic compound to be alkylated or acylated; and then
ii. contacting a liquid reaction mixture comprising said aromatic compound and said alkylating or acylating agent in the presence or absence of a non-aqueous solvent with the catalyst obtained from step (i) in a stirred batch reactor fitted with a reflux condenser under vigorous stirring, in the presence or absence of an inert gas bubbling through the reaction mixture, at effective reaction conditions;
iii. cooling the reaction mixture to a temperature about 30xc2x0 C., removing said catalyst from the reaction mixture by filtration and then separating the reaction products from the reaction mixture, and optionally washing the used catalyst by non-aqueous solvent; and if desired,
iv. reusing the used catalyst directly with or without drying for the subsequent reaction batch avoiding step (i), is disclosed.
Accordingly, this invention provides a process for the preparation of substituted aromatic compound represented by a formula
(R1R2R3R4)xe2x80x94Mxe2x80x94Yxe2x80x94(R5R6R7),
from substituted aromatic compound having formula:
(R1R2R3R4)xe2x80x94Mxe2x80x94H
with an alkylating or acylating agent represented by a formula:
(R5R6R7)xe2x80x94Yxe2x80x94X
to produce corresponding alkylated or acylated aromatic compound represented by a formula:
(R1R2R3R4)xe2x80x94Mxe2x80x94Yxe2x80x94(R5R6R7),
wherein, M is an aromatic nucleus such as single aromatic ring containing 6 C-atoms and 1 H-atom or fused two aromatic rings containing 10 C-atoms and 3 H-atoms or three fused aromatic rings containing 14 C-atoms and 5 H-atoms; R1, R2, R3 and R4 are groups attached to the aromatic nucleus, M; Y, which is a nucleus of alkylating or acylating agent, is selected from C6H2xe2x80x94CnH2n, C6H2xe2x80x94CO, CnH2nxe2x88x922, CmH2mxe2x88x924 and Cxe2x80x94CO; R5, R6 and R7 are groups attached to the nucleus of alkylating or acylating agent, Y; X is a halogen or hydroxyl chemical group; H is hydrogen; C is carbon; O is oxygen; n and m are integer numbers having value above zero and above one, respectively; using a basic anionic clay catalyst represented by a formula:
[(M2+)1xe2x88x92x(M3+)x(OH)2]x+.[Ayxe2x88x92]x/y. q H2O
where M2+ is a divalent cation selected from Mg2+, Zn2+, Ni2+, Co2+, Mn2+, Cu2+ or a mixture thereof; M3+ is a trivalent cation selected from Ga3+, In3+, Al3+ Fe3+ Cr3+or a mixture thereof; x is a mole fraction of trivalent cations in the range of about 0.05 to about 0.5; O is oxygen; H is hydrogen; Ayxe2x88x92 mis an anion; y minus is an anionic negative charge having a value of 1 minus or 2 minus; and q is a number of water molecules, as the water of hydration; and said catalyst having X-ray diffraction pattern similar to that of a typical hydrotalcite anionic clay material, with or without supporting it on a porous catalyst carrier; the process comprises:
i. pretreating said catalyst by contacting it with a halogen containing compound in the presence or absence of a non-aqueous solvent and optionally washing the pretreated catalyst with non-aqueous solvent or liquid aromatic compound to be alkylated or acylated, and then
ii. contacting a liquid reaction mixture comprising said aromatic compound and said alkylating or acylating agent in the presence or absence of a non-aqueous solvent with the catalyst obtained from step (i) in a stirred batch reactor fitted with a reflux condenser under vigorous stirring, in the presence or absence of an inert gas bubbling through the reaction mixture, at following reaction conditions: weight ratio of catalyst to alkylating or acylating agent in the range from about 0.01 to about 2.0, mole ratio of aromatic compound to alkylating or acylating agent in the range from about 0.1 to about 100, weight ratio of non-aqueous solvent to aromatic compound in the range from zero to about 100, reaction temperature in the range from about 10xc2x0 C. to about 300xc2x0 C., pressure in the range from about 0.5 atm to about 10 atm, gas hourly space velocity of inert gas bubbled through the liquid reaction mixture in the range from zero hxe2x88x921 to about 5000 hxe2x88x921 and reaction period in the range from about 0.02 h to about 100 h;
iii. cooling the reaction mixture to a temperature about 30xc2x0 C., removing said catalyst from the reaction mixture by filtration and then separating the reaction products from the reaction mixture, and optionally washing the used catalyst by non-aqueous solvent; and
iv. reusing the used catalyst directly with or without drying for the subsequent reaction batch avoiding step (i).
Each of R1, R2, R3 and R4 groups may be H or CnH2n+1 or CmH2mxe2x88x921 or C6H5 or CnH2nC6H5 or OH or OCnH2n+1 or OC6H5 or halogen or NO2 or NH2 or NHCnH2n+1 or N(CnH2n+1)2 or NHCOCnH2n+1 or NHCOC6H5 or CN or CHO or COOH or COOCnH2n+1 or COCnH2n+1 or SO3H or SO3CnH2n+1 or SH or alkyl mercapto group or aryl mercapto group and each of R5, R6 and R7 chemical groups may be H or CH3 or C2H5 or OH or OCH3 or OC2H5 or NO2 or halogen or NH2, wherein n and m are integers greater than or equal to 1 and 2, respectively, and C,H,N,O and S are chemical elementsxe2x80x94carbon, hydrogen, nitrogen, oxygen and sulfur, respectively.
The main finding of this invention is that, the said catalyst, which is basic in nature, shows high activity in the alkylation or acylation of aromatic compounds not only when the electron donating group, which is aromatic ring activating group, is present in the aromatic ring to be alkylated or acylated but also when the electron donating group is absent in the aromatic ring to be alkylated or acylated and hence the reaction temperature is low and/or the time required for completing the reactions is short.
Other important finding of this invention is that said solid catalyst can be separated easily and reused repeatedly in the process. Another important finding of this invention is that the alkylation or acylation of aromatic compound over said catalyst occurs with high reaction rates even in the presence of moisture in the reaction mixture containing aromatic compound to be alkylated or acylated, alkylating or acylating agent, solid catalyst and solvent, if used. Yet another important finding of this invention is that the pretreatment of the said catalyst with halogen containing compound in the step I of said process is essential for activating said catalyst.
Basic anionic clays Having hydrotalcite structure are well known in the prior art. Methods of the preparation of hydrotalcite-type basic anonic clays are also known in the prior art [ref. Cavani et al. Catalysis Today, vol. 11, page 173-301, (1991)].
In the said anionic clay catalyst, the anion, Ayxe2x88x92, may be mono or divalent anion, such as (CO3)2xe2x88x92, (OH)1xe2x88x92, (CH3COO)1xe2x88x92, (SO4)2xe2x88x92, (HSO4)1xe2x88x92, (HCO3)1xe2x88x92, (NO3)1xe2x88x92, (ClO4)1xe2x88x92, halide or other mono or divalent anion.
In the process of this invention, the pretreatment to said anionic clay catalyst may be effected by contacting it with a liquid halo organic compound in the presence or absence of non-aqueous solvent above room temperature for a period sufficient to activate the catalyst. The pretreatment to the said catalyst may also be effected by contacting it with a halogen compound in gaseous or vapor form, such as HCl, HBr, HF, Cl2, Br2, F2 or halo organic compound or a mixture thereof at or above room temperature for a period sufficient to activate the catalyst. The halo organic compound used in the catalyst pretreatment may be benzyl chloride or bromide, benzoyl chloride or bromide, acetyl chloride or bromide, halo hydrocarbons, other chloro, bromo and fluoro organic compounds or a mixture thereof.
In the process of the present inverition, the preferred reaction temperature may be between 20xc2x0 C. and 200xc2x0 C.; the preferred reaction pressure may be between 1 atm and 5 atm; the preferred reaction period may be between 0.05 h and 20 h; the preferred gas hourly space velocity of inert gas bubbled through the reaction mixture may be between 50 hxe2x88x921 and 500 hxe2x88x921 the preferred  wt. ratio of catalyst to alkylating or acylating agent may be between 0.03 and 0.9; the preferred mole ratio of aromatic compound to alkylating or acylating agent may be between 1.0 and 20; the preferred wt. ratio of non-aqueous solvent to aromatic compound may be between zero and 20; each of the preferred R1, R2, R3 and R4 chemical groups may be selected from hydrogen (H), alkane (CnH2n+1), olefinic (CmH2mxe2x88x921), phenyl (C6H5), alkoxy (OCnH2n+1), phenoxy (OC6H5), hydroxyl (OH), aldehydic (CHO), ketonic (RCO), amine (NH2), amide (CONH2), thio (SH) and sulfonic acid (HSO3) groups (wherein n and m are integers having value xe2x89xa71 and xe2x89xa72, respectively); each of the preferred R5, R6 and R7 chemical groups may be selected from hydrogen, alkane, olefinic, phenyl, halogen (Cl or Br or I or F), nitro (NO2) and cyano (CN) groups; the preferred chemical group X may be selected from Cl, Br and OH; the preferred divalent cation of the said catalyst may be selected from Mg2+ Zn2+ or a mixture thereof; the preferred trivalent cation of the said catalyst may be selected from Ga3+, In3+, Fe3+ or a mixture thereof; the preferred anion, Ayxe2x88x92, of the said catalyst may be selected from (CO3)2xe2x88x92, (OH)xe2x88x921 or a mixture thereof, the preferred mole fraction, x, of the trivalent cation of the said catalyst may be between 0.1 and 0.4; and the preferred halogen containing compound used for pretreating said catalyst in step (i) of the process may be selected from gaseous hydrogen halides, such as HCI and HBr, gaseous halogens, such as C2 and Br2 or from liquid halo organic compounds, such as benzyl chloride or bromide, benzoyl chloride or bromide, acetyl chloride or bromide.
The process of this invention can be carried out in a stirred batch reactor, fitted with a reflux condenser and arrangement for bubbling inert gas through the reaction mixture, known in the prior art for carrying out liquid phase reactions.
In the process of this invention, the main products formed are said alkylated or acylated aromatic compound and a by-product HX, wherein H=hydrogen and X=halogen or OH, depending upon the alkylating or acylating agent used.
In the process of this invention, the reactants namely aromatic compound and alkylating or acylating agent are converted partially or completely to the corresponding products.
The process of this invention may be carried out with or without using solvent, such as ethylene dichloride, nitrobenzene, nitromethane, chlorobenzene, n-hexane, n-heptane, n-octane or any other solvents. In the process of this invention, the role of solvent, if used, is to dissolve solid reactant or reactants, to dilute reactants and/or to facilitate the reaction between aromatic compound and alkylating or acylating agent. However, solvent may not be used in the process of this invention when both the reactants are liquids at said reaction conditions. Normally, said solvent is not converted in the process of this invention.
In the process of this invention, the role of inert gas bubbling continuously through the reaction mixture is to remove continuously said by-product from the reaction mixture so that the reverse reaction is avoided or minimized and the time required for completing the reaction is shortened. In the absence of bubbled inert gas, the reaction can still take place but with incomplete conversion and/or requiring longer period.
In the process of this invention, the role of the reflux condenser fitted with the reactor is to condense reactants and solvent, if used, and to return them back to the reaction mixture and allow the inert gas, which is continuously bubbling through the reaction mixture, along with said by-product to escape from the reaction mixture.
In the process of this invention, the reaction pressure above atmospheric pressure may be used to allow the reaction to be carried out at temperature higher than the normal boiling point of the reactants and/or solvent, by increasing the boiling point of said reactants and/or solvent with increasing the reaction pressure.
Said catalyst, used in the process of this invention, is heterogeneous with respect to the reaction mixture and can be removed from the reaction mixture simply by filtration and the removed catalyst, after washing with solvent or said liquid aromatic compound, which is to be alkylated or acylated, can be reused in the said process.
Said pre-treatment to said catalyst in step (i) of the process of present invention is essential for activating the catalyst so that the catalyst shows its high activity for catalyzing the alkylation or acylation reaction. The catalyst in the process of this invention can be easily separated from the reaction mixture simply by filtration. The used catalyst of this process can be reused in the process several times. The reused catalyst shows high activity in the process of this invention.
The role of said catalyst is to activate both the reactantsxe2x80x94aromatic compound and alkylating or acylating agent and thereby to increase rate of the reaction.
By the process of this invention, benzene (which does not contain any electron donating group) can be benzylated with benzyl chloride to diphenyl methane with 100% conversion of benzyl chloride, at a temperature of 80xc2x0 C. for a reaction period of 0.1 h and benzene can also be benzoylated with benzoyl chloride to benzophenone with 90% conversion of benzoyl chloride for a reaction period of 3 h.
The present invention is described with respect to the following examples illustrating the process of this invention for the alkylation or acylation of aromatic compounds using solid basic anionic clay catalyst, having hydrotalcite structure. These examples are provided for illustrative purposes only and are not to be construed as limitations on the process of this invention.
Definition of Terms Used in the Examples
Conversion of reactant (%)=mole % of the reactant converted to all products. All the ratios of aromatic compounds to alkylating or acylating agent are mole ratios. All the solid catalyst to alkylating or acylating agent and solvent to aromatic compound ratios are weight ratios.
The flow rates of gases are measured at 0xc2x0 C. and 1 atm pressure. Gas hourly space velocity (GHSV) is volume of gas, measured at 0xc2x0 C. and 1 atm pressure, passed through unit volume of the liquid reaction mixture per hour.
Ac and Aa represent aromatic compound to be alkylated or acylated and alkylating or acylating agent, respectively.